As Gun Star said, use the SRV scanner. When driving around, the scanner return will show a bunch of vertical blips in a pattern.
The pattern will be wide at first. Try to line up so the pattern is roughly centered on the scan. Head in that direction and you'll see the pattern shrink towards the middle of the scanner.
When you get close enough, you'll see a white dot on your radar. That's your target. Shoot it and you'll see sparks fly from it. It only take a few shots.
When the target explodes, get closer and you can scoop up the goodies.
You'll get the hang of it after the first one. It's just rinse and repeat after that.
The best place IMO is Dav's Hope. You can pick up a lot of manufactured mats at the abandoned mine and then wander off to collect the rocks. Just grab everything and you can use the mat traders to get what you're after.
You can get a load of mats from the Barnacles too. Much faster to fill up than surface prospecting, but it'll take a bit of travelling.